Electromagnet bobbin structure for vehicle brakes containing an abrasive wear surface

ABSTRACT

An electromagnet for use in electric vehicle brakes in which a bobbin for the electrical coil contains a flange of a friction material which engages the armature of the brake when the magnet is energized. The bobbin and coil assembly are inserted in the annulus of the housing between the inner and outer poles and the bobbin flange having the friction materials forms a snug fit with the housing and is held firmly in place by an epoxy material in the bottom of the annulus. The bobbin preferably contains a lug which extends into and/or through an opening in the bottom of the housing and protects the leads from the coil. The bobbin and coil assembly can be easily assembled in the annulus by merely pressing the bobbin in place with the flange having the friction material flush with the surface of the two poles, after the epoxy material has been placed in the annulus, thus providing an accurately faced electromagnet after the coil has been assembled therein without machining or grinding.

United States Patent 1191 Grove 1451 Aug. 14, 1973 ELECTROMAGNET BOBBIN STRUCTURE FOR VEHICLE BRAKES CONTAINING AN [57] ABSTRACT ABRASIVE WEAR SURFACE A l f I h l b ak n e ectromagnet or use an e ectnc ve ic e 1' es in [76] Inventor Leroy I g i 'jg iz which a bobbin for the electrical coil contains a flange awa n of a friction material which engages the armature of the [22] Filed; Nov, 10, 1971 brake when the magnet is energized. The bobbin and coil assembly are inserted in the annulus of the housing [2]] Appl' 197329 between the inner and outer poles and the bobbin flange having the friction materials forms a snug fit with [52] U.S. Cl. 335/281, 188/ 138 the housing and is held firmly in place by an epoxy ma- [51] Int. Cl. I-I0lf 7/08 rial in he bottom of the annulus. The bobbin prefera- [58] Field of Search 188/138 X, 164; bly contains a lug which extends into and/or through an 336/192; 335/281, 296, 297, 299 opening in the bottom of the housing and protects the leads from the coil. The bobbin and coil assembly can [56] References Cited be easily assembled in the annulus by merely pressing UNITED STATES PATENTS the bobbin in place with the flange having the friction material flush with the surface of the two poles, after 22 55 the epoxy material has been placed in the annulus, thus 3 244 944 4/1966 Birge:::........ 1 ss 13s x Pmvidmg accuately faced electmmagne after 3:476:223 11/1969 Hubbard 188/164 coil has been assembled therein Without machining of grinding. Primary Examiner-George Harris Attorney-Marmaduke A. Hobbs et al. 14 Claims 14 Drawing 1 1 I 1 l 40 p 55 p6 Patented Aug. 14, 1973 3 Sheets-Sheet 1 ATTORNEYS Patented Aug. 14, 1973 3 She'ets-Sheet 2 r INVENTOR.

- upon/c GROVE r r TTO YS Patented Aug. 14, 1973 3 Sheets-Sheet 3 I N VEN TOR.

M m w v1 MM All ATTORNEYS ELECTROMAGNET BOBBIN STRUCTURE FOR VEHICLE BRAKES CONTAININGJAN ABRASIVE WEAR SURFACE- In a conventional, hydraulically actuated brake, a pair of brake shoes are pivotally secured to a stationary brake back-up plate and are moved into contact with a brake drum by the actuation of a piston in a hydraulic brake cylinder responsive to fluid pressure applied to the brake cylinder. In an electrically actuated system, the brake shoes are moved by means responsive to an electrical current, such a system being exemplified by the United States Patent to Willian F. Penrose, US. Pat. No. 2,273,065. In these electrically operative systems, a lever arm is pivotally secured to the brake backup plate such that rotation of the lever arm causes movement of the brake shoes into contact with the brake drum. At the end of the lever arm is secured an electromagnet which is usually maintained in sliding contact with an armature plate which is secured to and moves with the brake drum. In a one piece cast iron drum and hub assembly, the face of the drum may serve as the armature plate. When the electromagnet is energized, it is magnetically attracted to the rotating armature plate, and, due to the friction between these two metal parts so attracted, a force is imposed on the magnet tending to move it in the direction of movement of the armature. This force is in turn transmitted by the lever arm to actuate the brake shoes into braking engagement with a brake drum.

The primary object of the present invention is to provide an improved and simplified design and construction of a brake electromagnet which is more reliable and much less expensive than those being producedin the present state of the art. It has been the current practice to construct an electromagnet consisting basically of a magnetic metal housing or body with two opposite magnetic poles consisting of a center core and outer ring connected at the base and separated at the friction face by a recessed annulus. A coil of magnet wire wound on an insulating plastic coil form is disposed in the annulus of the housing with lead wires extending outward through an opening in the side of the housing. This coil assembly is either cemented into place, clamped in place, or encapsulated in a potting compound to retain it in the housing. The lead wire opening is usually sealed with potting compound or silicone rubber to protect the coil. A frictional wear pad or abrasive-filled potting compound is used to fill the void above the coil and bobbin assembly and to become a part of the magnet frictional face. After the cement or potting compound has cured, it is necessary to grind or sand the face of the magnet to achieve a flat face in one plane. The relatively large amount of material and labor involved in the present state of the art will be apparent when compared with the magnet of this invention. It is therefore another object of my invention to avoid or eliminate these foregoing difficulties and to produce a superior brake magnet capable of long, trouble-free service at optimum performance.

Further objects and advantages of the present invention will become apparent from the following description and accompanying drawings, wherein: e

FIG. 1 is an elevational view of a vehicular electric brake backing plate, brake shoes and operating mechanism of the type which may be used in combination with the electromagnet of the present invention;

FIG. 2 is a cross-sectional view of my electromagnet, the section being taken on line 22 of FIG. 1;

FIG. 3 is an elevational view of one side of a bobbin used in the production of the bobbin and coil assembly incorporated in my electromagnet structure;

FIG. 4 is a cross-sectional view of the bobbin shown in FIG. 3, the section being taken on line 4-4 of the latter figure. I

FIG. 5 is an enlarged elevational view of a portion of the bobbin shown in the preceding figures;

FIG. 6 is a perspective view of the bobbin shown in the preceding figures;

FIGS. 7, 8 and 9 show perspective views illustrating the method followed in completing the bobbin and coil assembly involving the bobbin shown in FIGS. 3 through 6;

FIGS. 10, 11 and 12 are perspective views illustrating the manner in which the bobbin and coil assembly of FIGS. 7 through 9 are assembled in the housing of the magnet;

FIG. l3 is a plan view of a modified form of a bobbin embodying the present invention; and

FIG. 14 is a cross-sectional view of the bobbin shown in FIG. 13, the section being taken on line 14-14 of the latter figure.

Referring more specifically to the drawings and FIG. 1 in particular, numeral 10 indicates generally the brake assembly, including a brake operating mechanism l2 and a brake drum 14 which is attached to and normally forms a part of the wheel structure of the vehicle in which the brake is used. The brake assembly includes a backing plate 16 on which brake shoes 18 and 20 are pivotally mounted and movably secured thereto or restrainedby spring-loaded retaining pin assemblies 22 and 24, respectively. The brake shoes contain friction material 26 and 28 bonded to the external surface of the brake shoes, and engage the internal surface of drum 14 when the brake is applied. An adjustment screw 30 interconnects the brake shoes, which are yieldably retained in their retracted positionfro'm the brake drum by springs'32 and 34. v

The brake actuating mechanism for applying brake shoes 18 and 20 into braking engagement with the drum consists of an electromagnet 40, a lever 42 connected at one end to the magnet and pivotally mounted on a pin 44, which in turn is secured to backing plate 16. Lever 42 swings onpin 44 and is curved in an offset manner to pass around the drum axis and to position the electromagnet at a point l80.degreesfrom pin 44. Arm 42 includes an extension or short ann 46.carrying a pin 48 on a swivel block 50, which bears against the adjacent ends of the brake shoes. The magnet is operated in conjunction with a radial positioned armature 51 connected directly to or fonning an integral part of brake drum 14', on a plane parallel with backing plate 16. The magnet 40 which is adapted to frictionally engage the face of the armature when energized, is mounted on arm 42 by an attachment and retainer consisting generally of two fingers 52 and 53 joined at right angles to the arm and extending through holes 54 and 55, respectively, in the magnet. A force transmitting bushing 56, which fits freely in the counterbore of hole 54 but will not pass through the hole, is secured on the end of finger 52 and retains the magnet on the fingers. The two holes are offset in opposite directions from the center axis of the magnet housing, and bushing 56 and finger 52 transmit the forces created between the armature and magnet to arm 42 for actuation of the brake, while finger 53 prevents any substantial rotation of the magnet on its center axis. A coil spring 57 reacting be tween lever 42 and the magnet urges the magnet into light pressure contact with the armature.

With the armature and the brake drum l4 rotating in a counterclockwise direction, electromagnet 40, when energized, will be magnetically attracted to and frictionally engage the armature and will be moved to the right, thereby moving pin 48 to the left so that it pushes against the end of brake shoe 18 to move the shoe outwardly into braking engagement with the internal surface of drum 14. The engagement of the brake shoe 18 with the drum in turn develops a self-energizing force on shoe 18, which is transmitted through screw 30 to brake shoe to cause the latter shoe to move into braking engagement with the internal surface of drum 14. With the rotation of the armature plate and brake drum in the clockwise direction, the action just described is performed in reverse with the electromagnet moving to the left to cause pin 48 to engage the adjacent end of the brake shoe 20, which in turn, through screw 30, actuates brake shoe [8. When the electromagnet is released or deenergized, the two springs 32 and 34 disengage the brake shoes from the drum, returning them and the electromagnet to the position illustrated in FIG. 1.

In my invention the electromagnet 40 has been simplified to its required basic elements, consisting of a metal housing 60 to carry the magnetic flux and a bobbin and coil assembly 62 to create the magnetic field. The metal housing is constructed of powdered iron formed and compressed to high density in its finished size and shape and sintered at high temperatures to impart its structural strength, and is produced on automated machinery, ready for assembly without further machining. The bobbin and coil assembly consists of the magnet wire 64 and lead wires 66 and 68 assembled on a novel multi purpose bobbin 70. The construction and functions of this bobbin result in an electromagnet which is much more reliable and far less expensive than those being produced in the present state of the art. This bobbin, as illustrated in FIGS. 3, 4 and 5, has a cylindrical center 72 and flanges 74 and 76, is nonmagnetic and electrically non conductive, structurally strong, suitable for high temperature environment, abrasive to serve as a frictional face, and adapted to be molded economically to close tolerances. While it is not intended to limit the scope of this invention to any particular material, one example of a suitable material for the bobbin is a glass filled polycarbonate plastic such as General Electric Company's Lexan. Other suitable materials are polyurethane and a natural or synthetic rubber based friction material. It fulfills all the above requirements and can be injection molded for the most economical high production.

This one piece molded bobbin is designed to enable the bobbin, at little or not extra cost, to serve several distinct functions. The bobbin is an electrically insulating coil form for the magnet wire and the upper bobbin flange 74 is designed to serve as a part of the wear and friction face 78 of the magnet. This bobbin flange face imparts a thin film of plastic and fine glass abrasive to the face of the armature to form an abrasive film barrier between the metal-to-metal contact of the magnet and armature, thus helping to prevent galling and resultant drum scoring.

FIGS. 13 and 14 illustrate a simplified form of the bobbin in which boss 90 is omitted from flange 76, the other parts of the bobbin remaining essentially the same as the previously described embodiment.

The method of fabricating the coil is illustrated in FIGS. 7, 8 and 9. On the bottom flange 76, of the bobbin is a slot 80 of special configuration to serve as a start lead wire 82 exit in winding. This avoids taping the start lead of the magnet wire to the inside of the bobbin flange to protect against shorted turns. When the coil has been wound to the required number of turns, the winding machine operator can cut the magnet wire and pull it through a large slot 84, against without taping, to prevent the unravelling of the winding. The elimination of taping the start and finish leads on each coil significantly increases theproduction output of the operator and winding machine. After the coil is wound, the insulated lead wires 66 and 68 are attached to the magnet wire leads, the connections insulated and the two lead wires are inserted in the larger slot 84 near the periphery of the lower flange 76. With the lead connections secured by tape 86 to the outside diameter of the magnet wire coil and the insulated lead wire secured in the flange slots, no pulling stress on the lead wires can be transmitted to the lead wire connections.

In the preferred embodiment a boss 90 may be molded on the exterior of the bottom flange around the large slot 84 to provide an insulated bushing for the lead wires when they are subsequently inserted through the exit slot in the bottom of the housing annulus. The periphery 92 of upper bobbin flange 74 and an annular surface 93 of similar depth in the bore of the bobbin are molded to a size to provide an interference fit with the outside and inside diameters of the annulus 96 in housing 60, the lower flange 76 and the balance of the bobbin bore being a clearance fit in the annulus of the housing, and the overall length of the bobbin being less than the depth of the annulus.

The bobbin design facilitates the efficient and rapid final assembly of the magnet, fully illustrated in FIGS. 10 to 12. In the final assembly of the bobbin and coil assembly to the housing, the two lead wires 66 and 68 are inserted in an exit slot 100 in the bottom of the annulus of the housing. A small amount of room temperature curing thixotropie epoxy or adhesive 102 is placed in the bottom of the housing annulus. The bobbin and coil assembly is dropped into annulus 96 up to the interference fit of the bobbin bore and upper flange periphery 92 with the lead wires or lead wire bushing boss aligned with the exit slot 100 in the bottom of annulus 96. A simple power press can then be used to press the bobbin and coil assembly into the desired face relationship with the metal housing. Epoxy or adhesive 102 flows into and seals the lead wire exit slot and locks the bobbin and coil assembly into this face relationship permanently, and no face grinding of the magnet is necessary.

The completed magnet with my novel construction gives improved reliability, increased life, and optimum braking performance, and the frictional wear face will not powder or disintegrate as sometime happens with a poured epoxy face. The frictional surface 78 will not loosen and separate, and lead wires 66 and 68 are rigidly supported and sealed from the inside to provide maximum protection from water, moisture and road dirt and slush.

While only one embodiment of my electromagnet has been described in detail herein, various changes and modifications may be made without departing from the scope of the invention.

I claim:

1. An electromagnet for use in electric vehicle brakes having an armature, comprising a metal housing having a center pole and a peripheral pole and an annulus therebetween, a bobbin having a center member with an axial hole therethrough and two radially extending, spaced flanges one of said flanges having a wear surface adapted to engage the armature of said brake and containing an abrasive to form an abrasive film barrier between the metal-to-metal contact of the magnet and armature, and having a configuration substantially the same as the opening of said annulus for forming a snug fit within the opening of said annulus, and a coil of wire on said bobbin for energizing said magnet.

2. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said one flange contains a friction material at the wear surface thereof.

3. An electromagnet for use in electric vehicle brakes as defined in claim 1 wherein said annulus has a depth greater than the width of said bobbin so that when said one flange of said bobbin is flush with the poles of said housing there is a space between the bobbin and the bottom of said annulus and a potting compound is disposed in said space for rigidly retaining said bobbin in position in said housing.

4. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which a pair of leads is attached to the coil of wire.

5. An electromagnet for use in electric vehicle brakes as defined in claim 4 in which a boss is disposed on said other flange of said bobbin and includes a pair of radially extending slots, one of said slots being adapted to receive the end of the coil of wire before it is wound on the bobbin and the other slot being disposed in said boss and adapted to receive and protect said leads from said coil.

6. An electromagnet for use in electric vehicle brakes as defined in claim 5 in which said boss on said other flange partially surround the slot in which said leads are located and the inner portion of said housing contains an opening extending therethrough for receiving said leads and said boss.

7. An electromagnet for use in electric vehicle brakes as defined in claim 6 in which an epoxy at least partially fills the space between said bobbin and the inner wall of said annulus and extends into the hole in which said boss and leads are located in said housing.

8. An electromagnet for use in electric vehicle brakes as defined in claim 4 in which said leads are connected to the two ends of said coil of wire and a layer of tape holds the connection between the leads and the two ends firmly against the periphery of said coil.

9. An electromagnet for use in electric vehicle brakes as defined in claim 8 in which a layer of insulating material is interposed between said connection and said coil.

10. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said one flange containing the friction material is thicker than the other flange of said bobbin.

11. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said bobbin is constructed of plastic material.

12. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which the material of said bobbin contains polyurethane and said abrasive is glass.

13. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said bobbin is constructed of rubber based material.

14. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which the entire structure of said bobbin is impregnated with said abrasive. k 

1. An electromagnet for use in electric vehicle brakes having an armature, comprising a metal housing having a center pole and a peripheral pole and an annulus therebetween, a bobbin having a center member with an axial hole therethrough and two radially extending, spaced flanges one of said flanges having a wear surface adapted to engage the armature of said brake and containing an abrasive to form an abrasive film barrier between the metal-to-metal contact of the magnet and armature, and havinG a configuration substantially the same as the opening of said annulus for forming a snug fit within the opening of said annulus, and a coil of wire on said bobbin for energizing said magnet.
 2. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said one flange contains a friction material at the wear surface thereof.
 3. An electromagnet for use in electric vehicle brakes as defined in claim 1 wherein said annulus has a depth greater than the width of said bobbin so that when said one flange of said bobbin is flush with the poles of said housing there is a space between the bobbin and the bottom of said annulus and a potting compound is disposed in said space for rigidly retaining said bobbin in position in said housing.
 4. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which a pair of leads is attached to the coil of wire.
 5. An electromagnet for use in electric vehicle brakes as defined in claim 4 in which a boss is disposed on said other flange of said bobbin and includes a pair of radially extending slots, one of said slots being adapted to receive the end of the coil of wire before it is wound on the bobbin and the other slot being disposed in said boss and adapted to receive and protect said leads from said coil.
 6. An electromagnet for use in electric vehicle brakes as defined in claim 5 in which said boss on said other flange partially surround the slot in which said leads are located and the inner portion of said housing contains an opening extending therethrough for receiving said leads and said boss.
 7. An electromagnet for use in electric vehicle brakes as defined in claim 6 in which an epoxy at least partially fills the space between said bobbin and the inner wall of said annulus and extends into the hole in which said boss and leads are located in said housing.
 8. An electromagnet for use in electric vehicle brakes as defined in claim 4 in which said leads are connected to the two ends of said coil of wire and a layer of tape holds the connection between the leads and the two ends firmly against the periphery of said coil.
 9. An electromagnet for use in electric vehicle brakes as defined in claim 8 in which a layer of insulating material is interposed between said connection and said coil.
 10. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said one flange containing the friction material is thicker than the other flange of said bobbin.
 11. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said bobbin is constructed of plastic material.
 12. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which the material of said bobbin contains polyurethane and said abrasive is glass.
 13. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which said bobbin is constructed of rubber based material.
 14. An electromagnet for use in electric vehicle brakes as defined in claim 1 in which the entire structure of said bobbin is impregnated with said abrasive. 